Acute abdomen

The term acute abdomen refers to a sudden, severe pain in the abdomen that is less than 24 hours in duration. It is in many cases an emergent condition requiring urgent and specific diagnosis. Treatment usually involves surgery.

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Causes

The differential diagnosis of acute abdomen includes but is not limited to:

1. Acute appendicitis.
2. Acute peptic ulcer and its complications.
3. Acute cholecystitis.
4. Acute pancreatitis.
5. Acute intestinal ischemia (See Section Below.)
6. Diabetic Ketoacidosis.
7. Acute Diverticulitis.
8. Ectopic Pregnancy with tubal rupture.
9. Acute peritonitis.
10. Bowel perforation with free air or bowel contents in the abdominal cavity.
11. Acute ureteral colic.
12. Bowel volvulus.

Peritonitis

Acute abdomen is occasionally used synonymously with peritonitis. This is not incorrect; however, peritonitis is the more specific term, referring to inflammation of the peritoneum. It is diagnosed on physical examination as rebound tenderness, or pain upon removal of pressure rather than application of pressure to the abdomen. Peritonitis may result from several of the above diseases, notably appendicitis and pancreatitis.

Ischemic Acute Abdomen

Vascular disorders are more likely to affect the small bowel than the large bowel. Arterial supply to the intestines is provided by the superior and inferior mesenteric arteries, (SMA and IMA respectively) both of which are direct branches of the aorta.

The Superior Mesenteric Artery supplies:

1. Small bowel.
2. Ascending and proximal 2/3 of the Transverse colon.

The Inferior Mesenteric Artery supplies:

1. Distal 1/3 of the Transverse colon.
2. Descending colon
3. Sigmoid colon.

Of note, the splenic flexure, or the junction between the transverse and descending colon, is supplied by the most distal portions of both the Inferior Mesenteric Artery and Superior Mesenteric Artery, and is thus referred to medically as a watershed area, or an area especially vulnerable to ischemia during periods of systemic hypoperfusion, such as in shock (medical).

Acute abdomen of the ischemic variety is usually due to:

1. A thromboembolism from the left side of the heart, such as may be generated during atrial fibrillation, occluding the SMA.
2. Nonocclusive ischemia, such as that seen in hypotension secondary to heart failure may also contribute, but usually results in a mucosal or mural infarct, as contrasted with the typically transmural infarct seen in thromboembolus of the SMA.
3. Primary mesenteric vein thromboses may also cause ischemic acute abdomen, usually precipitated by hypercoagulable states such as polycythemia vera.

Clinically, patients present with diffuse abdominal pain, bowel distention, and bloody diarrhea. On physical exam, bowel sounds will be absent. Laboratory tests reveal a neutrophilic leukocytosis, sometimes with a left shift, and increased serum amylase. Abdominal radiography will show many air-fluid levels, as well as widespread edema.

Acute ischemic abdomen is a surgical emergency. Typically, treatment involves removal of the region of the bowel that has undergone infarction, and subsequent anastomosis of the remaining healthy tissue.

Workup

Patients presenting to A&E or the ER with severe abdominal pain will almost always have an Abdominal x-ray and / or a CT scan. These tests can provide a differential diagnosis between simple and complex pathologies. It can also provide evidence to the doctor whether surgical intervention is necessary.

Patients will also most likely receive a CBC/Diff, looking for characteristic findings such as neutrophilia in appendicitis.